JPS63181258A - Cell electrode - Google Patents

Abstract

PURPOSE:To remarkably increase the current collecting capability of a metal assembly and obtain the excellent performance by using a specific block copolymer containing a specific hydrogenation/denaturation block copolymer as a binder for a conductive paint film. CONSTITUTION:A block copolymer described below and containing a hydrogenation/denaturation block copolymer combined with molecule units hydrogenated and/or having a carboxylic acid group or its derivative group is used as a binder for a conductive paint film. The block copolymer is constituted of a polymer block I mainly made of one vinyl aromatic compound and a polymer block II mainly made of one conjugate diene compound. Thereby, the conductive paint film containing the hydrogenation/denaturation block copolymer as the binder can increase the current collecting capability of a metal assembly remarkably. Since the hydrogenation/denaturation block copolymer is excellent in adhesive property, a current collector coated with the conductive paint film has the high current collecting performance, and a cell electrode excellent in the mechanical characteristic, particularly peel strength, can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a novel secondary battery, and more particularly to a small and lightweight secondary battery.

[Conventional technology] In recent years, electronic devices have become smaller and lighter, and as a result, there is a strong demand for batteries that serve as power sources to be smaller and lighter.In the field of secondary batteries, small-sized lithium batteries and other Although lightweight batteries have been put into practical use, since these are secondary batteries, they cannot be used reversibly, and their field of use has been limited. On the other hand, in the field of secondary batteries, lead batteries and nickel-cadmium batteries have conventionally been used, but both have major problems in terms of miniaturization and weight reduction. From this point of view, a new group of electrode active materials that utilize the intercalation or doping phenomenon of layered compounds, which is a reaction type essentially different from that of conventional nickel-cadmium batteries, lead-acid batteries, etc., are attracting attention.

For example, Japanese Patent Publication No. 55-2062 discloses current collectors coated with various conductive coatings.

[Problems to be Solved by the Invention] This new electrode active material does not cause any complicated chemical reactions during its charging and discharging, and is therefore expected to have extremely excellent charge-discharge cycle performance. However, it has not yet been put into practical use.

One of the factors hindering the practical application of such prescribed electrode active materials is the problem of the current collection performance of the current collector. Here, current collection performance refers to the ability to efficiently transfer current to and from the electrode active material, and if a current collector with low current collection performance is used, the basic characteristics of the electrode active material No matter how good the current collector is, it is not possible to effectively express its performance, and an electrode made of such a current collector and an electrode active material cannot have a satisfactory current collecting performance. One of the influencing factors is an increase in contact resistance that occurs as the active material peels off from the current collector. In other words, the decrease in current collection performance is due to the adhesiveness between the current collector and the active material, so it is an excellent idea to improve the current collection performance by increasing the adhesiveness between the current collector and the active material to reduce contact resistance. This is an extremely important issue for creating electrodes that

The present invention has been made to solve the above-mentioned problems and provide a battery electrode with excellent performance.

[Means and effects for solving the problems] According to the present invention, there is provided a battery electrode comprising, as constituent elements, at least an electrode active material and a current collector coated with a conductive coating film, wherein the conductive coating film as a binder, at least one polymeric block consisting mainly of a vinyl aromatic compound, and at least one
Polymer block II mainly composed of conjugated diene compounds
Hydrogenated, modified, or modified hydrogenated block copolymer in which a block copolymer consisting of is combined with a hydrogenated and/or molecular unit containing a carboxylic acid group or a derivative group of 7. A non-aqueous battery electrode is provided.

The block copolymer referred to in the present invention is, for example,
■-■, I-to1. n-l-11-1, (1-U)4
Si.

It is a vinyl aromatic compound-conjugated diene compound block copolymer having a structure such as l-11-1-11-1.

This block copolymer preferably contains 5 to 60% by weight of a vinyl aromatic compound, more preferably 10% by weight.
~40% by weight. Furthermore, referring to the block structure, polymer block I mainly composed of a vinyl aromatic compound is a vinyl aromatic compound polymer block,
or has a structure of a copolymer block of a vinyl aromatic compound and a conjugated diene compound containing more than 50% by weight, preferably 70% by weight or more of a vinyl aromatic compound, and further contains a conjugated diene compound as a main component. The polymer block (2) is a conjugated diene compound polymer block, or contains more than 50% by weight of a conjugated diene compound.

Preferably, it has a structure of a copolymer block of a conjugated diene compound and a vinyl aromatic compound containing 70% by weight or more. In addition, these polymer block I mainly composed of a vinyl aromatic compound and the polymer block II mainly composed of a conjugated diene compound are based on the distribution of the conjugated diene compound or vinyl aromatic compound in the molecular chain in each polymer block. may be random, Chibird (in which the monomer component increases or decreases along the molecular chain), partially block-like, or any combination thereof. When there are two or more polymer blocks (1) each containing a conjugated diene compound as a main component, each block may have the same structure or may have a different structure.

As the vinyl aromatic compound constituting the block copolymer, one or more types are selected from, for example, styrene, α-methylstyrene, vinyltoluene, p-tert-butylstyrene, etc. Among them, styrene is preferred. Also,
As the conjugated diene compound constituting the conjugated diene compound, one or more types are selected from, for example, butadiene, isoprene, 1,3-pentadiene, 2,3-dimethyl-1,3-butadiene, etc. Among them, butadiene , isoprene, and a combination thereof are preferred, and the microstructure in the polymer block mainly composed of a conjugated diene compound can be arbitrarily selected,
For example, in a polybutadiene block, the 1,2-microstructure is preferably 10-80%, more preferably 10-65%.

The number average molecular weight of the block copolymer is preferably 5,0
00 to 1,000,000, more preferably 10
．． 000~800,000, optimally 30,000~
300.000, and the molecular weight distribution (ratio of weight average molecular weight to number average molecular weight) is preferably 10 or less.

The molecular structure of the block copolymer provided in the present invention may be linear, monobranched, radial, or any combination thereof, and any production method may be used as long as it has the above-mentioned structure. It doesn't matter what you can get.

For example, by the method described in Japanese Patent Publication No. 40-23708, a vinyl aromatic compound-conjugated diene compound block copolymer is synthesized in an inert solvent using a lithium catalyst, etc., and the block copolymer of the present invention is synthesized. It can be served as

This block copolymer can be used, for example, in Japanese Patent Publication No. 42-8704
The hydrogenated block copolymer of the present invention can be obtained by hydrogenation in an inert solvent in the presence of a hydrogenation catalyst by the method described in Japanese Patent Publication No. 59-133203. At that time, at least 50% or more, preferably 80% or more of the aliphatic double bonds based on the conjugated diene compound of the vinyl aromatic compound-conjugated diene compound block copolymer are hydrogenated, so that the conjugated diene compound is the main component. The polymer block can be morphologically converted into an olefinic compound polymer book H. In addition, regarding the hydrogenation rate of aromatic double bonds based on the vinyl aromatic compound copolymerized into the block A mainly composed of a vinyl aromatic compound and the polymer block H mainly composed of a conjugated diene compound as necessary. There is no particular limit, but if the hydrogenation rate is 2
The amount of unhydrogenated aliphatic double bonds contained in this hydrogenated block copolymer, which is preferably 0% or less, can be easily determined using, for example, an infrared spectrophotometer or a nuclear magnetic resonance apparatus. Can be done.

As mentioned above, a conductive coating film containing a hydrogenated block copolymer as a binder can significantly enhance the current collecting ability of a metal current collector. Since this hydrogenated block copolymer has excellent heat resistance, the current collector coated with this conductive coating exhibits stable current collection ability from a low temperature of -40°C to a high temperature of 80°C. can do.

The modified block copolymer of the present invention includes a block copolymer having the above-mentioned structure before hydrogenation and α.

Grafting reaction of β-unsaturated carboxylic acids, their anhydrides, or esters (hereinafter abbreviated as α,β-unsaturated carboxylic acids) in a melt or solution state with or without the use of a radical initiator. It can be obtained by The manufacturing method is not particularly limited in the present invention, but methods that cause the obtained modified block copolymer to contain undesirable components such as gel, or that reduce its fluidity and deteriorate processability are not applicable. This is not preferred, but a method in which additives such as antioxidants are added in an extruder or the like and the modification reaction is carried out under melt-mixing conditions that substantially do not generate radicals is preferred.

The modified block copolymer that can be provided in the present invention preferably has 10 parts by weight or less of α,β-unsaturated carboxylic acids added per 100 parts by weight of the block copolymer. - If the amount of unsaturated carboxylic acids added is more than 10 parts by weight, it tends to have an adverse effect on the electrical properties of the conductive coating film. On the other hand, if the amount added is less than 0.05 part by weight, adhesiveness tends to decrease.

Here, α and β can be provided during the grafting reaction.
- Examples of unsaturated carboxylic acids include malein m,
maleic anhydride, fumaric acid, itaconic acid, acrylic acid,
Acrylic acid ester, crotonic acid, cis-4-cyclohexane-1,2-dicarboxylic acid and its anhydride, endo-cis-bicyclo-[2,2,11-5-heptene-
Examples include 2,3-dicarboxylic acid and its anhydride, maleimide, and among these, maleic anhydride is preferred.

Further, usable organic peroxides include, for example, dicumyl peroxide, di-tert-butyl peroxide, tart-butyl cumyl peroxide, 2.5-
Dimethyl-2,5-di(tert-butylperoxy)
Hexane and 2,5-dimethyl-2,5-di(ter)
t-butylperoxy)hexyne-3, n-butyl-4
, 4-bis(tert-butylperoxy)valerate, 1.1-bis(tart-butylperoxy)-3
, 3,5-trimethylcyclohexane, etc., and can be suitably selected from among these.

The obtained modified block copolymer may be ionomerized with a monovalent or higher valence metal ion, and furthermore, unreacted α, β-unsaturated carboxylic acids may remain in the modified block copolymer. It may be removed completely.

As mentioned above, a conductive coating containing a modified block copolymer as a binder can significantly enhance the current collecting ability of a metal current collector. Since this modified block copolymer has excellent jIi adhesion, the current collector coated with this conductive coating exhibits high current collection performance, and also has excellent mechanical properties and
In particular, a battery electrode with excellent peel strength can be provided.

The modified hydrogenated block copolymer of the present invention comprises a hydrogenated block copolymer having the above-mentioned structure, and α.

β-unsaturated carboxylic acid or its anhydride, ester, etc. (
(hereinafter abbreviated as α,β-unsaturated carboxylic acids) in the presence or absence of an organic peroxide. The reaction may be carried out in either a molten state or a solution state, and the modified hydrogenated block copolymer contains 0% per 100 parts by weight of the hydrogenated block copolymer.
．． Preferably, 5 to 10 parts by weight of α,β-unsaturated carboxylic acids are added.If the amount of α,β-unsaturated carboxylic acids added is more than 10 parts by weight, the electrical properties of the conductive coating film will be affected. This is not desirable because it has a negative effect.

The method for producing the modified hydrogenated block copolymer is not particularly limited in the present invention, but the modified hydrogenated block copolymer obtained may have a structure deviating from the above-mentioned characteristics, or may have a gel or other structure. Manufacturing methods that include undesirable components or that significantly increase the melt viscosity and deteriorate processability are undesirable.As an example of a preferred manufacturing method, for example, the above-mentioned process using an extruder at a temperature of 150 to 350°C is undesirable. Hydrogenated block copolymer, α, β-unsaturated carboxylic acids,
If necessary, there is a method of melt-kneading an organic peroxide and radically modifying it. The obtained modified hydrogenated block copolymer may be ionomerized with a monovalent or higher valent metal ion.

In addition, in the modified hydrogenated block copolymer thus obtained, unreacted α,β-unsaturated carboxylic acids or derivatives thereof generally remain as unreacted substances; may be completely removed or left as is.

As mentioned above, a conductive coating film containing a modified hydrogenated block copolymer as a binder can significantly enhance the current collecting ability of a metal current collector. Since this modified hydrogenated block copolymer has excellent heat resistance and adhesive properties, the current collector coated with this conductive coating can be heated from a low temperature of -40°C to 80°C.
It is possible to provide a battery electrode that stably exhibits power supply ability up to high temperatures, and has excellent mechanical properties, particularly peel strength.

The conductive coating film referred to in the present invention is mainly composed of the binder and the conductive filler. Carbon and metal powder can be considered as the conductive filler, but graphite, acetylene black, carbon black, and mixtures thereof are preferable. The weight ratio of the conductive filler to the binder (x=conductive filler weight/binder weight) is not particularly limited, but is preferably 0.5≦X≦2. The current collector is mainly a metal current collector, and examples thereof include foil, net, expanded metal, punched metal, etc. of metal such as copper, aluminum, titanium, stainless steel, and nickel.

In the present invention, the current collector coated with a conductive coating film is
When the current collector is metal foil, the coating liquid consisting of the above-mentioned binder, conductive filler and solvent (toluene, microsol, etc.) is applied with a coater. In such cases, it can be easily obtained by dipping or spraying.

As mentioned above, if a current collector coated with the conductive coating film of the present invention is used, it is important to reduce the contact resistance with the active material layer and further improve electrode performance.

The electrode active material used in the present invention is not particularly limited, but examples include MnO2, M2O3°V2O
5, V6O13, Fe2O3, Fe30a, L:x-
×>CoO2+Lic+-x)・NiO2, TiS2.
TiS3. MoB2. Fe53. CuF2+N
Inorganic compounds such as iF2, carbon fluoride, graphite, vapor-grown carbon fibers and/or pulverized products thereof, PAN-based carbon fibers/or pulverized products thereof, pitch-based carbon fibers, and/or pulverized products thereof.
or carbon materials such as its crushed products, polyacetylene, poly-
Examples include conductive polymers such as p-phenylene.

When the electrode active material is in powder form, it can be molded by mixing it with a binder liquid and then coating and drying it on the current collector of the present invention.

The battery electrode of the present invention may be used as a positive electrode or a negative electrode depending on the electrode active material.

When assembling a nonaqueous battery using the battery electrode of the present invention,
The electrolyte of the non-aqueous electrolyte is not particularly limited, but an example is LiCl! On, LiBFa, LiAs
F6゜CF3SO3Li, LiPF6. Lil,
LiAllCl! a, NaC1!04sNaBF4.
Nal, (n-Bu)nN@lJ'04. (n-
Bu)4N@BFa.

Examples include KPF b. In addition, examples of organic solvents used in the electrolytic solution include ethers, ketones, lactones, nitriles, amines, amides, sulfur compounds, chlorinated hydrocarbons, esters, nibonates, nitro compounds, and phosphorus. Acid ester compounds, sulfolane compounds, etc. can be used, and among these, ethers, ketones, nitriles, chlorinated hydrocarbons, carbonates, and sulfolane compounds are preferred.

Representative examples of these include tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, anisole, monoglyme, acetonitrile, propionitrile, 4-methyl-2-pentanone, butyronitrile, valeronitrile, benzonitrile, 1,2- Dichloroethane, γ-butyrolactone, dimethoxyethane, methylformate, propylene carbonate, ethylene carbonate, dimethylformamide, dimethyl sulfoxide,
Dimethylthioformamide, sulfolane, 3-methyl-
Examples include sulfolane, trimethyl phosphate, triethyl phosphate, mixed solvents thereof, etc., but are not necessarily limited to these.

Furthermore, if necessary, the battery is constructed using parts such as a separator, a current collector, a terminal, and an insulating plate. In addition, the structure of the battery is not particularly limited, but may include a positive electrode, a negative electrode,
Examples include a paper type battery having a single layer or multiple layers of separators, or a cylindrical battery having a positive electrode, a negative electrode, and, if necessary, a separator wound into a roll.

[Effects of the Invention] As explained above, the battery electrode of the present invention can reduce the connection resistance with the active material layer and further improve the electrode performance, and is a small, lightweight, high-altitude non-aqueous battery electrode. Extremely useful as a battery electrode.

[Examples] Hereinafter, the present invention will be explained in more detail with reference to Examples and Comparative Examples. In addition, the properties of poly, breaking strength, breaking elongation, 300
The % modulus was determined based on JIS K 6301 using No. 3 dumbbells and under the conditions of a tension of 500 mm/win.

In addition, the peeling property test is based on the goban test method JIS D 02.
It was conducted based on 02. Furthermore, the contact resistance was measured by connecting to the measurement circuit shown in FIG. 1 using a gold vapor-deposited electrode.

In Fig. 1, E, V, and A are respectively a DC power supply, a voltmeter,
B, C, and D each represent an electrode of an ammeter, and C and D are concentric circles. Moreover, X is a sample for measurement.

First, the block copolymers used in Examples and Comparative Examples will be explained.

(1) (Polystyrene-polybutadiene) It has a 4Si structure, the amount of bound styrene is 18% by weight, the amount of 1.2-vinyl bonds in the polybutadiene part is 33%, and the number average molecular weight is 105.
．． 000 and a molecular weight distribution of 1.33 was synthesized and designated as block copolymer A.

Next, it has a structure of polybutadiene-polystyrene-bolybutadiene-polystyrene, the amount of bound styrene is 22% by weight, and the amount of 1,2-vinyl bonds in the polybutadiene part is 29% by weight.
%, number average molecular weight 111,000, molecular weight distribution 1.1
A block copolymer of No. 2 was synthesized and designated as block copolymer B.

Furthermore, it has a polystyrene-polybutadiene-boristyrene structure, with a bound styrene content of 40% by weight, a 1,2-vinyl bond content in the polybutadiene portion of 51%, a number average molecular weight of 123,000, and a molecular weight distribution of 1.26. A polymer was synthesized and designated as block copolymer C. Breaking strength and breaking elongation of the block copolymer C obtained above: 300
% modulus is 150kgf/cm2.1000% each
, 30 kgf/cm2.

The above block copolymers A, B, and C were modified with maleic anhydride without using peroxide. Modified block copolymers E and F were obtained by adding 16 parts by weight, 0.66 parts by weight, and 1.32 parts by weight. The breaking strength, breaking elongation, and 300% modulus of the obtained modified block copolymer F were each h 130
kgf/cm2.1000%.

It was 40 kgf/cm2.

(2) Hydrogenated polybutadiene-polystyrene-
It has a hydrogenated polybutadiene-polystyrene structure, with a bound styrene content of 30% by weight, 1,2-vinyl bonds in the polybutadiene portion before hydrogenation of 44%, and a number average molecular weight of 79,000. Molecular weight distribution 1.05, hydrogenation rate 99%
A hydrogenated block copolymer G was synthesized using a Ti-based hydrogenation catalyst described in JP-A-59-133203.

(3) Polystyrene - hydrogenated polybutadiene -
Has a polystyrene structure, with a bound styrene content of 43% by weight
, the amount of 1,2-vinyl bonds in the polybutadiene moiety before hydrogenation is 52%, the number average molecular weight is 91,000, and the molecular weight distribution is 1.
．． 04, a hydrogenated block copolymer with a hydrogenation rate of 96% was synthesized using the aforementioned 74 series hydrogenation catalyst, and this was designated as hydrogenated block copolymer H. Obtained hydrogenated block copolymer H
The breaking strength, breaking elongation, and 300% modulus of *2
70kgf/cm2.600%.

It was 50 kgf/cts2.

(4) Polystyrene-hydrogenated polybutadiene)
-4Si structure, the amount of bound styrene is 18% by weight, the amount of 1,2-vinyl bonds in the polybutadiene part before hydrogenation is 29%, the number average molecular weight is 42,000, the molecular weight distribution], 4
1. The hydrogenated block copolymer with a hydrogenation rate of 97% was mixed with the above Ti
It was synthesized using a hydrogenation catalyst, and this product was used as a hydrogenated block copolymer.

(5) Hydrogenated block copolymer G obtained above.

A modification reaction was carried out using H, I, maleic anhydride, and lysicumyl peroxide, and modified hydrogenated blocks to which 0.51 parts by weight, 1.9 parts by weight, and 0.12 parts by weight of maleic anhydride were added, respectively, were obtained. Polymers J and L were obtained. The breaking strength, breaking elongation,
300% modulus is 220kgf/cm2.6 each
00%, 60 kgf/cm2.

Next, the conductive coating films used in Examples and Comparative Examples will be explained.

(6) Carbon black powder with a particle size of 705 g (manufactured by Industrial Carbon Black Co., Ltd.,
RAVEN 410) was mixed with 10 parts by weight of a toluene solution (10 wf% concentration) of modified hydrogenated block copolymer J to prepare a coating liquid. Apply this coating liquid to a thickness of 1
A film was coated on both sides of a copper foil measuring 10 cm x 1000 cm with a thickness of 2 l on each side.

(7) 2 parts by weight of carbon black powder with a particle size of 70 parts was added to a toluene solution of modified hydrogenated block copolymer J (10 wt.
% concentration) to prepare a coating solution. This coating liquid is 15 parts thick and the size is 10 cm x 1000
A film was coated on both sides of CYS aluminum foil at a thickness of 2 layers per side.

Example 1 Average particle size 2 ILs+ NoLi1113C00,95S
! 10.04202 1 part by weight of powder contains 0.075 part by weight of graphite with an average particle size of 5 and an average particle size of 0.03.
Mix 0.025 parts by weight of acetylene black,
Fluororubber methyl isobutyl ketone solution (8 degrees 4wt
%) was added and mixed and stirred to obtain a coating liquid. Said (
This coating solution was applied and dried using aluminum foil coated with the conductive coating film obtained in step 7) as a base material, and an electrode having a film thickness of 100 layers was obtained. From this electrode film body, lc shoes X5c+s
was cut out and used as the positive electrode. Regarding the above electrode, as a result of measuring the contact resistance through the conductive film of the aluminum foil current collector and the Li+, o3Coo, 9sSno, o4202 coating, it was found that 5
Ω/C113. Further, Table 1 shows the results of 0 or more indicating that the peeling properties of such electrodes were extremely good.

Next, commercially available petroleum-based needle coke (K made by Koa Oil Co., Ltd.
OA-5J Cake) was milled with a ball mill to an average particle size of 10.
The above fluororubber was ground in methyl isobutyl ketone solution (concentration 5 wt%) to 1 part by weight of the ground material.
) was added thereto and mixed and stirred to obtain a coating liquid. Said (
This coating solution was applied to a copper foil coated with the conductive coating film obtained in step 6) as a base material and dried to obtain an electrode having a film thickness of 60 μm. A 1 cm×5 cm piece was cut out from this electrode film body and used as a negative electrode. The contact resistance of the above electrode was measured through the conductive film of the copper foil current collector and the needle coke coating, and the result was 0.2 Ω/ctm3. Table 1 shows the results of 0 or more indicating that the peeling properties of such an electrode were extremely good.

A battery shown in FIG. 2 was assembled using 0.6M-Lieβ64 propylene carbonate as the electrolyte. The overvoltage of this battery during charging and discharging at 10 A (current density 2 mA/cm) was 0.02 V.

Examples 2 to 9 Completely the same as Example 1 except that in (6) and (7) above, modified hydrogenated block copolymer J was replaced with E, F, G, H, I, and L. The battery was assembled and evaluated using a unique method. The results are shown in Table 1.

Comparative Examples 1 and 2 Completely the same as Example 1 except that in (6) and (7) above, modified hydrogenated block copolymer J was replaced with A, NBR (40% by weight of acrylonitrile part, 60% by weight of butadiene part). Battery assembly and evaluation were performed in the same manner. The result is the first
Shown in the table.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram for measuring contact resistance, and FIG. 2 is a sectional view of a secondary battery used in an example of the present invention. 1... Positive electrode, 2... Negative electrode, 3.3'... Current collector rod, 4.4'... SUS net, 5.5'... External electrode terminal, 6... Battery case, 7... Separator, 8... Electrolyte or solid electrolyte, E... DC power supply, ■... Voltmeter, A... Ammeter, B, C, D... Electrode, X...・Sample for measurement.

Claims (1)

[Claims] (1) A battery electrode consisting of a current collector in which an electrode active material is coated with a conductive coating film, the conductive coating film serving as a binder containing a polymer block mainly composed of at least one vinyl aromatic compound. Water obtained by bonding a block copolymer consisting of I and a polymer block II mainly composed of at least one conjugated diene compound with a hydrogenated and/or simple molecule containing a carboxylic acid group or a derivative group thereof. A battery electrode comprising an added block copolymer, a modified block copolymer, or a modified hydrogenated block copolymer.